1. Field of the Invention
The present invention generally relates to an information recording/reproducing apparatus that records information on and/or reproduces information from optical disk recording media allowing rewriting of information.
2. Description of the Related Art
Conventionally, optical disk apparatuses, which are information recording/reproducing apparatuses, generally perform recording while rotating a recording medium at a CLV (Constant Linear Velocity). In the CLV method, the relative rates of a recording medium and a laser beam are always constant. Thus, once optimum recording conditions such as a recording power and a recording pulse width are determined, it is unnecessary to vary the recording conditions over the entire surface of a recording medium. Hence, normally, test writing is performed in a specific area of the innermost track portion while changing the power of a laser beam in stages for each predetermined step. The area on which test writing is performed is reproduced, and the optimum recording power is determined based on the characteristic values of a reproduction signal. Then, recording is generally performed on the entire recording medium at an identical CLV by using the optimum recording power.
In the CLV method, however, since the rotational speed is controlled such that the linear velocity becomes constant, it is necessary to increase the rotational speed for the inner tracks. Thus, it becomes more difficult to control the rotation as the linear velocity becomes larger. That is, since it is necessary to vary the rotational speed, higher rotational torque is required. This causes problems such as an increase in the size and/or cost, and an increase in noise and/or vibration. There is also a problem in that, since a waiting time is required until the speed is changed at the time of seeking, the access time becomes longer.
Therefore, with the increase in the recording speed, there have been proposed methods of recording information on a recording medium while rotating the recording medium at a CAV (Constant Angular Velocity), and the ZCLV method that divides a recording medium into several zones in the radial direction and records information on the recording medium while varying the linear velocity in stages. Among these, the CAV method offers various advantages, for example: since the rotation of a recording medium is controlled by a constant angular velocity (number of revolutions), speed control is easier compared to the CLV method; since a low rotational torque will suffice, it is possible to use a small and low-cost motor; and since waiting time for changing speed is not required, it is possible to reduce the access time.
In the CAV method and the ZCLV method, on the other hand, the number of RPMs in the inner tracks is not originally increased. Accordingly, the recording linear velocity is lower in the inner tracks and higher in the outer tracks. For example, a case is assumed where a recording operation is performed according to a CAV method in which the number of RPMs is constant and the recording linear velocity in the outer tracks is equivalent to 24-speed. In this case, the recording linear velocity in the inner tracks is approximately 10-speed, and the actual recording linear velocity is varied from 10-speed to 24-speed. Accordingly, considering a case of recording information on the entire surface of a recording medium, for the most part, recording must be performed at a linear velocity that is different from the recording linear velocity in the specific inner track area on which test writing is performed.
Generally, in organic dye DVD-R media and phase-change type rewritable (RW) media on which pits (marks) are formed by heat modes, the pulse width of a recording pulse sequence and the recording power of a laser beam at the time of recording are optimized at a specific recording linear velocity. Hence, the states of marks and spaces to be formed vary at different recording linear velocities. That is, there have been problems in that, if the pulse width and/or the recording power are not correctly set, jitter characteristics are degraded for the reasons as follows: the amount of heat required for formation of marks may be excessive or insufficient; the average length of marks may be varied due to the difference between an optimum decomposition temperature and a heating temperature achieved at each mark length; and the mark width is increased/decreased depending on the mark length since a uniform mark width is not achieved due to variation in the optimum pulse width.
In order to solve the above-mentioned problems, there has been proposed an information recording apparatus that varies recording power based on a writing clock frequency that is proportional to recording linear velocity (Japanese Laid-Open Patent Application No. 11-296858).
There has also been proposed an information recording apparatus that: at the time of factory shipment, divides the entire area (including a user area) of a recording medium into several zones and stores in storing means the optimum recording power level for each of the zones obtained by test writing of each of the zones, performs test writing in PCAs (Power Calibration Areas) provided in an inner track portion and an outer track portion before actual recording so as to obtain the rate of change between the optimum recording power levels stored in the storing means and the optimum recording power obtained by test writing in the PCAs, and corrects the optimum recording power levels stored in the storing means by calculation in order to realize optimum recording over the entire area of the recording medium (Japanese Patent No. 3164763).
However, the conventional information recording apparatuses as mentioned above still include problems. The information recording apparatus described in Japanese Laid-Open Patent Application No. 11-296858 has a problem in that recording of good quality cannot be achieved unless recording characteristics (i.e., required recording power and/or other recording conditions) of a recording medium are in exact proportion to recording linear velocity. As a matter of course, there is no such a disk recording medium, and variation in each recording medium is inevitable. Additionally, as represented by the information recording apparatus described in Japanese Patent No. 3164763, in the case where optimum recording power in the entire area of a recording medium is corrected by calculation using a certain coefficient based on results of test writing in PCA, there is a problem in that variation in each recording medium, variation in areas of the recording medium, and variation in the environment (e.g., temperature and humidity) at the time of recording are not considered.